1. Field of the Invention
The present invention relates to a vent valve, and more particularly to a vent valve for a fuel pump which is effective for purging air out of a fuel passage in a vehicle fuel pump.
2. Prior Art
Conventionally, a vehicle fuel pump is generally provided with a vent valve for purging air out of a fuel passage in a vehicle fuel pump. One of such conventional vent valves is shown in FIG. 4.
As shown, this conventional vent valve 1 comprises a barrel 2 formed to be of substantially cylindrical shape and a steel ball 3 inserted from an opening 4 into the barrel 2, this steel ball effecting as a valve body. The steel ball 3 opens or closes a valve opening 5 of the barrel 2 according to the output of fuel. That is, the vent valve 1 is placed in a vent passage branched off from the fuel passage in a manner that the valve opening 5 is directed upward. The steel ball 3 is at a lower position in the barrel by its own weight, when the fuel pump is started to operate. Thus, air is ejected out of the pump through the valve opening 5, and then, as the vent passage is filled with fuel, the steel ball 3 closes the valve opening 5.
When, however, the barrel 2 is set into the vent passage, the barrel is pressed into the vent passage, and, accordingly, a closed wall at the upper portion of the barrel 2 can deform because the barrel 2 is of substantially cylindrical shape. Therefore, some fuel may leak when the pump sends out the fuel, because the barrel 2 is deformed and a gap is formed between a valve seat portion 6 around the valve opening 5 and the steel ball 3, making it impossible for the steel ball 3 to close the valve opening 5 hermetically.